Mashable has taken a look at three paywalled sites: the Dallas Morning News, the Economist and the Honolulu Civil Beat.

It has talked to community editors on the titles about how they promote stories via social media without incurring the wrath of angry readers who follow links to then find they are blocked by a paywall.

Like any good social media strategist, transparency is key for Hudson.

He designates whether a link is behind the paywall when posting it on Facebook or Twitter.

The Economist

Social media helps the site reach subscribers, regular readers and new readers by the means most convenient to them, while providing an opportunity to spark discussions around the Economist’s coverage areas.

“Readers who are empowered to participate are likely to spend more time with the site, return more often and become more active advocates of our work,” [Mark Johnson, The Economist's community editor] says.

With the metered model, Johnson and other web producers can share any articles on social networks without experiencing the backlash of readers’ inability to access the site. Perhaps more importantly, they’re able to bring in more traffic.

“Referrals to the site from social networks, and the pageviews generated by such referrals, have grown almost every month since our social strategy began,” Johnson says. “Nor is this growth slowing. If anything, it’s speeding up.”

Honolulu Civil Beat

Online-only local news site the Honolulu Civil Beat is coming up on the one-year anniversary of its launch.

Though content is and always has been free through email, the site initially gave only partial access to visitors who came through social networks.

Beginning January 2011, however, all visitors can read all articles until they visit regularly enough to be asked to become a member.

“We figured, if they’re reading us that much they would be happy to become a member, and we’d be happy to have them,” says Dan Zelikman, the Civil Beat‘s marketing and community host.

There is no specific threshold number. Rather, the site runs a custom program that asks a reader to subscribe based on how often and how much he or she reads.

“Basically, if you read a couple of times a week, it will take a while before we ask you to register,” Zelikman says.

Reading access aside, the Civil Beat’s subscription model fosters community by only allowing members to comment on articles. In addition, subscribers experience the site without advertising, a perk that’s particularly popular with the community.